T124 Blade Sharpening

[Jared Greenberg]

First post, searched around and couldn't find an answer to my questions so here it is:

I have Minimax's T124 lathe. I am mostly turning maple, with the occasional piece of ash and birch thrown in.

After turning to the finished product the piece comes out quite rough, and usually need to start out with a 40 grit to get it smooth, then go through various grits to get the finish I am after. I have looked on other photos on different threads and the finished turning seems to be a lot smoother than what I am producing (maybe because they are softer woods?)

I currently use a standard bench grinder, with Lee Valley's honing compound. I was wondering if a belt sander would be better for this application.

Any sharpening tips or suggestions on how to get it to be smoother after turning (so less sanding is required) would be greatly appreciated.

[Richard Wolf]

Jared, are you turning with hand tools or are you using the copy attachment?
It sounds like you may be using the copy device which tends to leave a rougher finish. Alot depends on feed rate, material, cutter design and depth of cut. If you could show a pic of what you are turning, I may be able to help you.

Richard

[Jim Becker]

In addition to Richard's comments, copy-lathes in general do not provide the same off-the-tool finish as you will see with hand-turned items in the turning forums. The "copy" part does a great job turning to specification, but since the tooling remains in a stationary position (relative to the cutting edge and the workpiece) there is no opportunity to manipulate things for a finishing cut as you can by hand. Copy-lathes are production tools to turn out (pardon the expression...) identical items quickly, but they will invariably require additional sanding.

That said, you shouldn't be getting a surface so rough (in most cases) that requires you to start with such course abrasives as 40 grit. I can believe 80 grit average to start, but not 40 grit. That tells me that perhaps the cutter (which operates as a scraper) is not properly sharpened, resulting in "chunks" of material being removed rather than a reasonably clean cutting action being affected on the workpiece. Further, it could also mean you're trying to take too much of a cut with each pass. Many, many light cuts are a better choice for a smoother surface.

Many of these cutters have some kind of bevel under the edge with a flat top. While you occasionally need to restore the bevel, most of your sharpening/honing should be to the flat top of the cutter and with minimal material removal. A good diamond hone used with reasonable frequency should do the trick.

Jim
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[I'm going to leave this thread here in General Woodworking for now rather than move it to the Turning Forum. While it does refer to turning, the particular tool is a a bit different assuming you're using it as a copy-lathe]

Jim

[Jared Greenberg]

Thanks for the responses. We are turning baseball bats, and we are using metal templates. We are producing about 1700-2000 per year on this machine. With growth, I am looking to speed up the process, and cut down on our sandpaper budget!

I don't get a lot of tear out per say, and the wood doesn't come off in chucks. I have tried turning it every way, fast, slow, take off a lot, take off a little to get the best results. Just by using this machine I am betting that it is my sharpening methods that lead to this, or lack thereof.

I am turning at 1200RPM, one thing I haven't tried is turning the piece slower, do you think around 700RPM might produce better results?

I am attaching pics of the knife that is used on the lathe. I just don't think the bench ginder is doing the trick at all, the 'faces' of the knife doesn't come out with a mirrow finish, that is why I thought going to a vertical bench sander might be a better option.

On the top and bottom pics it is the bottom knife, in the middle it is the lower blade.

http://f9g.yahoofs.com/groups/g_8079124/90d3/__sr_/26c2.jpg?grYAiSGBr9N87xQN
http://f9g.yahoofs.com/groups/g_8079124/90d3/__tn_/1fae.jpg?grAQiSGBC66uOrlo (http://finance.ph.groups.yahoo.com/group/MiniMax-USA/photos/view/90d3?b=3)
http://f9g.yahoofs.com/groups/g_8079124/90d3/__sr_/931c.jpg?grAQiSGBYb6llYBH

[Richard Wolf]

For some reason I can't see your pictures. Any way, turning baseball bats on the T124 should work out very well. I have made some cutters with custom profiles to match some of my turnings. You need some 1/2 sq. tool steel from a machine supply and some time on a grinder. With something like a baseball bat you may even be able to use an insert cutter. If the cutting point doesn't line up with the styllus, you may have to shift the template. Like Jim said, you should be able to start with 80 grit. paper.

Richard

[Jared Greenberg]

We are using blades/knives from Minimax, so that is fine, just that the work is rough.

We have a bunch of templates for each model, so that is set up as we have been using this machine for 3 years.

Can you explain insert cutter.

[Jim Becker]

Along the line of Richard's suggestion...you could create new cutters that have tips that are canted for more of a shearing cut by grinding them with the "top" at an angle on the horizontal axis. You'd have to make each pass in the same direction, but the cut "should" be cleaner.

[Jared Greenberg]

Ok, you just lost me.

[Richard Wolf]

We are using blades/knives from Minimax, so that is fine, just that the work is rough.

Can you explain insert cutter.

Okay, first, you may think the problem is not with the cutters that you purchased from MiniMax, but their copy cutters are designed for detailed copy work and not mass removal of wood. If you are not satisfied with the quality of your finished work, and you don't have flexing or vibration, which you shouldn't on a baseball bat, the problem has to be the cutters.

Second, this is an insert cutter;www.grizzly.com/products/g7036. Yes it is designed for metal, but will work well on wood. The good thing is if it works out for you, you will not have to spend time sharping.

Third, I realize that your templates are working, but if you use a cutting tool which now has a different point of contact, in relation to your styllus, you will have to make an adjustment to the postion of the template or you will no longer get an exact reproduction.

Richard

[Jim Becker]

Ok, you just lost me.

For shear cutting, the edge doing the cutting needs to be at an angle to the wood. This produces more of a "shaving". Since I don't believe you can rotate the cutter in your copy mechanism (maybe I'm wrong...), to get there, you'd have to grind the business end of the cutter to provide that angle.

To better understand what I mean, take an ordinary chisel in your hand. Hold it straight out from your body and perfectly horizontal. Now, slightly rotate your wrist so that the cutting edge of the chisel is higher on one side than the other side, but the tool itself is still level and straight out from your body. That's what I'm suggesting will give a cleaner finishing cut at the lathe. If you can't turn the tool to do this, you'll need to reshape the cutter. And your passes across the bat will always need to be toward the lower edge of the cutter.

But try the insert cutters that Richard speaks about. The carbide inserts will last a long time and may help you get where you want to go. Try different shapes, etc., until you find what works best for your bats and the material they are made of.

[Jared Greenberg]

The knife on both sides had its edges on an angle, I believe they are 10 or 15 degrees.

Since the billet is much bigger than the actual bat especially at the handle, the wood basically is taken off in 3 passes. One to the left, then one to the right and a final pass taking off approx 1/4" of wood on the final pass, wouldn't this be considered 'detail' work since I'm not taking off much stock.

Is the insert cutter an actual 'blade'? Would that link on grizzly.com actually work, or would I have to shape it to work for the specific application.

As far as the templates go, we use a measurement on the knob (which is at the tail) to reproduce the bat to the specific dimensions each time. So there is some adjusting to knife depth when we switch templates. We only have to adjust usually a few hundreths, bigger or smaller.

Thanks guys.

[Jim Becker]

Taking 1/4" off in a pass, outside of initial roughing off the corners of a square billet is A LOT of material to be cutting at one time even if you are moving really slow...a lot of the tooling edge is fully engaged with the wood. At least in my experience. For the best surface, your last pass should be taking off minimal material...it's a finishing cut, no matter what your method.

[Dick Strauss]

Jared,
I agree with Jim...1/4" is a lot to take off in one pass in scraping mode. The typical amount is 1/32" or less for a final pass using a scraper freehanded. I would assume you could get away with a little more with captive bits but I definitely wouldn't try 1/4" if you want a smoother surface.

You can buy HSS toolbits from Enco or other distrubutors for very little money. Then you can create custom bits (radii and angle) that work better for your particular jobs.

Do the MM cutting bits come to a point or very small radius? If so, a larger radius will work much better for your application!!!

Good luck,
Dick

[Jared Greenberg]

The blank start of round, the mill dowels them to about 2.75", on the first pass with the roughing knife on the set up, we redowl them to about 2.6-2.65 so they fit into the busing. So we aren't taking off any corners at all.

I will try to post the pics again.

http://f9g.yahoofs.com/groups/g_8079124/90d3/__tn_/26c2.jpg?grAp7SGBv2iWtzwV (http://finance.ph.groups.yahoo.com/group/MiniMax-USA/photos/view/90d3?b=2)

It isthe bottom knife. When it is use with the lathe, it is turned over. We have grounded a little off the front edge to form a flat surface, so there really isn't a point.


(http://finance.ph.groups.yahoo.com/group/MiniMax-USA/photos/view/90d3?b=1)

[Jared Greenberg]

http://f9g.yahoofs.com/groups/g_8079124/90d3/__sr_/931c.jpg?gro47SGBhwSPlYBH

[Jared Greenberg]

Do the MM cutting bits come to a point or very small radius? If so, a larger radius will work much better for your application!!!

Can you explain 'radius'. This bit comes to a point, would I need to rework it for a better result?

[Jared Greenberg]

Anyone have any further thoughts?

[Steve Clardy]

My suggestion is to remove all but a 1/16th or less.
Then the 16th for a final pass.
I have a Hempel CH-12. My last pass is around a 1/16th and is fairly smooth. When sanding, I start with 100 grit.

Speed up your machine on the last pass.